The Over Voltage Protection relay is basically just a relay that switches power to the fuel and ABS computers. What makes it special is a zener diode connected between the output and ground. If the supply voltage goes too high, say because of failure of the regulator inside the alternator, then the zener conducts and blows the fuse on top of the relay, protecting the computers.

The common cause of failure of the relay is bad solder joints on the printed circuit board inside. If you can use a soldering iron it's easy to open up the relay can and run over all the joints inside.

The N3 component you refer to sounds like the fuel computer, don't forget that your car's KE injection system is a mechanical system with some added electronic aids, one of which is the idle speed control. Most cars will run with the electronics out altogether, but starting and idling may be poor.

Your symptoms are typical of OVP failure, the other give away is illumination of the ABS light.